The present invention relates to joint prostheses, and more particularly it relates to the field of knee prostheses.
The term xe2x80x9cknee prosthesisxe2x80x9d applies to artificial joint systems intended to replace the natural joint constituted by the conformation of the bottom epiphysis of the femur, by the conformation of the complementary top epiphysis of the tibia, and also by the femoro-patellar element.
In the prior art, a large number of proposals have been made that apply to the above technical field.
Total prostheses have thus been proposed that are said to be xe2x80x9clinkedxe2x80x9d in that they make use of two complementary parts which are united by a physical hinge system, such as at least one pin, constituting the artificial pivot system enabling the knee to bend in a direction that is perpendicular to the sagittal or antero-posterior plane.
Prostheses have also been proposed that are said to be xe2x80x9cfreexe2x80x9d which are constituted, unlike the above prostheses, on the basis of two elements for fitting respectively to the bottom epiphysis of the femur and to the top epiphysis of the tibia for the purpose of co-operating by relative sliding while being maintained in surface contact in particular via natural internal and external lateral ligaments, and without making use of any physical hinge link between the two elements.
In reality, prostheses whether xe2x80x9clinkedxe2x80x9d or xe2x80x9cfreexe2x80x9d are designed to satisfy a specific joint-restoration requirement corresponding to a joint problem that needs to be overcome or compensated.
That is why a very large number of technical solutions have been proposed, each setting out to resolve a specific joint problem.
Such prostheses must certainly be considered as having provided solutions that are practical, suitable, and acceptable.
However, with the hindsight now available to practitioners, it can be considered that the prostheses that are presently proposed, and more particularly those of the free type, do not make it possible to maintain antero-posterior stabilization, nor to maintain the relative rearward displacement or sliding of the bottom epiphysis of the femur relative to the top epiphysis of the tibia during flexing, which displacement is known as xe2x80x9crollbackxe2x80x9d, while nevertheless making partial rotation possible as allowed by the natural knee joint.
However, it is becoming ever more clear that these requirements correspond to anatomical needs which it is important to maintain when prosthetically restoring a joint, at least for the purpose of reducing the ligament fatigue that such prostheses can cause.
The object of the invention is to satisfy that requirement by proposing a novel total knee prosthesis in the form of a single unit which is characterized by implementing complementary technical means between the femur prosthetic element and the tibia prosthetic element, which complementary technical means are designed to perform their own functions without interfering with the basic functional relationship between the condyles of the femur element and the glenoid cavities of the tibia element.
The total knee prosthesis of the invention is of the type comprising:
a U-shaped femur prosthetic element defining a housing for engaging the resectioned epiphysial portion of a femur and having an anterior portion defining a trochlea by its front face and a distalo-posterior portion defining two condyles; and
a tibia prosthetic element comprising a base for fitting to the resectioned epiphysial portion of a tibia and an insert mounted on the base and presenting, facing the femur prosthetic element, two glenoid cavities for co-operating with the condyles;
wherein:
the femur prosthetic element includes, between the condyles, a block presenting, in its outside face relative to the housing, a lug connecting to the trochlea and adjacent to a notch from which a convex bearing surface extends as far as the end portion of the block; and
the insert and the tibia prosthetic element include a sagittally-oriented elevation between the glenoid cavities and defining, relative to the front edge of said insert, an antero-posterior stabilization projection that is engaged in the notch when the prosthesis is in the extended position and that is connected to a concave sliding ramp extending as far as the rear edge of the insert to co-operate with the facing convex bearing surface when the prosthesis is in the extended position so as to define a gap of section that increases from the zone where the projection engages in the notch, all the way to said rear edge.